With the increase of capacity of a large-sized permanent magnet machine, internal losses of the permanent magnet machine also increase correspondingly, thus causing a temperature rise of the permanent magnet machine to be over-high, and further adversely affecting safe and stable operation of the permanent magnet machine. Although ventilation and cooling of the electric machine in a radial direction thereof or mixed ventilation and cooling in the radial and axial directions may meet the heat dissipating capability requirements of the large-sized permanent magnet machine, an effective material utilization rate of the large-sized permanent magnet machine is decreased due to the presence of a radial ventilation duct, and the weight and cost of the large-sized permanent magnet machine may be increased.